For me it depends on my training partner. If I catch a good clean submission then I will let it go and let them transition from it before they tap (while sparring).
If I get it and they defend, thats where it depends on the partner. Bigger stronger or higher ranking partner I may try to complete the sub, a smaller weaker or inexperienced partner i will just transition to something else.
for example:
Ive been getting alot of kimuras lately and alot of time in sparring I dont just rip into the submission so by me going slower it gives the training partner the time to grab the gi, belt, leg whatever thier defense is. So I know unless the guy is crazy stronger than me I can jerk the hell out of it until I complete it. But this leaves room for injury if I jerk too hard. That is why bigger guy I might try to jerk it a couple times to loosen thier grip but not go ape shit crazy on them. Smaller person I just transition to another position becuase I know in my mind I would have jerked it and gotten it for sure.
Im also the same on chokes I will not hold a choke no matter how deep it feels for more than 15 to 20 seconds. I hate when guys squeeze this shit out of my face trying to get a choke they dont have, and I dont want to be that guy so I let go if the pressure is obviously on their face and if I feel like its deep and they arent turning colors or tapping by around 20 seconds I let go.