Soviets were generally tactically inept in WW2, but wanted rapid advance
First, let's quickly look at the Red Army situation before WW2 and in early months of the conflict in the East. The Red Army was expanding in late 1930's and early 1940's as were practically all European (and even world) armies, preparing for the conflict that seemed inevitable. Rapid expansion introduces the problem of having enough competent officers and NCOs to lead new units. This problem was further exacerbated with the Tukhachevsky Affair and consequent purge of the Red Army, which left it practically leaderless and without much of competent trainers of troops. As a consequence, disaster happened in the first few months of the war, with further loss of experienced officers, this time as KIA or MIA .
Now, Soviet general-staff (Stavka) and to a lesser extent commanders of fronts, armies and corps, did purify themselves from incompetent officers fairly quickly (in 1941 and early 1942) . But the problem was deep rooted, down to regimental, battalion and company level. Most of junior officers didn't know how to fight, they had to be trained on the job, which is the worst kind of training for military - mistakes were paid with blood.
Consequently, while Soviet offensives from late 1942 onward were usually planned with considerable strategic and operational skill, on tactical level they were often crude and sacrificed lives of men in the first echelon in order to achieve quick success, thus saving lives of those in second echelon and reserve. The usual pattern would be heavy artillery fire, and then advance of infantry, sometimes supported by tanks and self-propelled guns, in order to breach the line . This advance would more often then not be a simple mass charge, without developed small units tactics, especially early and mid war . But if done sufficiently rapidly, mechanized and cavalry forces could be inserted trough the breech before German armored & mechanized reinforcements arrived, thus creating opportunity for envelopment and encirclement, the favorite Soviet strategy.
Now, considering Soviet Shtraftbats, or penal battalions and other penal units, official Soviet statistics says that 427 910 men or 1,24 % of all those serving in Red Army passed trough them. The average monthly casualties (KIA, WIA, MIA) in 1944 for penal units were 14 191 men, which scaled to proportion, is 3 to 6 times more than casualties in non-penal units. This of course makes sense, shtrafniki were there to "expunge their crimes with blood". This would of course depend on the local commander (Pavel Batov was supposedly notorious for this), but generally what they could expect is to be sent to the most dangerous places, and to lead the attack on prepared positions.
As for mine clearing and general tasks of military engineers and sappers, Soviets did have lot of specialized units for those tasks. On paper, they were well equipped and trained. Also, Soviet infantry, at least in theory, should have had basic mine clearing training, enough to create paths trough German minefields. Therefore, the tactic of deliberately sending men into minefields in order to detonate them and create passage for other units is not justified, especially since Soviets actually didn't have unlimited reserves of manpower, and faced shortages even in 1942-42, due to massive casualties and limited recruitment potential (large parts of Soviet Union occupied). This goes even for shtrafniki, if Soviet government wanted to kill off these men, they would have done that unceremoniously, without the need to send them to the front. However, what is possible and plausible is the situation where the local commander, in order to save time, sends penal battalion(s) to attack trough the minefield, calculating that incurred loses would be far higher if they waited for combat engineers and allow the enemy to reinforce the position. This would be in line with the aforementioned Soviet line of thinking, with relatively crude tactics but grandiose strategic goal in mind. Such situations would likely develop in the middle of an offensive operation, for example suddenly coming to a well defended objective that could not be bypassed but must be taken quickly.
