In my experience it seems that most people will tell you that it is unwise to force a garbage collection but in some cases where you are working with large objects that don\
There are few general guidelines in programming that are absolute. Half the time, when somebody says 'you're doing it wrong', they're just spouting a certain amount of dogma. In C, it used to be fear of things like self-modifying code or threads, in GC languages it is forcing the GC or alternatively preventing the GC from running.
As is the case with most guidelines and good rules of thumb (and good design practices), there are rare occasions where it does make sense to work around the established norm. You do have to be very sure you understand the case, that your case really requires the abrogation of common practice, and that you understand the risks and side-effects you can cause. But there are such cases.
Programming problems are widely varied and require a flexible approach. I have seen cases where it makes sense to block GC in garbage collected languages and places where it makes sense to trigger it rather than waiting for it to occur naturally. 95% of the time, either of these would be a signpost of not having approached the problem right. But 1 time in 20, there probably is a valid case to be made for it.