It would be a nightmare to lose self checkout at Target. It would be a blessing to lose it at CVS. It can be done very well or very poorly.
The other big difference in smoothness of experience is having sufficient staff to come and deal with problems. Firstly, because user or machine error will always be non-negligible, but also because age challenges are quite common too. It's frustrating queueing and seeing a good 4 or 5 machines in a blocked state (and sometimes abandoned due to it) and there being no or insufficient staff around to unblock them