A bus station works well if it is really close to the town centre or else services can serve the two centre and the bus station. Particularly good if they provide layover facilities, waiting room etc. There are some places, eg Kidderminster, where most services serve stops at the town centre and terminate at the bus station. At others, eg Canterbury, Doncaster, Lincoln, they are close to the town centre and often the only stop in the town centre, therefore used by everyone. Notably at these places virtually every service actually terminates here so it is a complete focal point for everything. Sometime they can get a bit crowded - but these are good bus stations for their towns.
In other places the bus station is slightly to one side of the town centre and services from some directions have town centre stops as well whereas others don't. Bedford is an example, again virtually every service terminates, those heading south over the bridge have stops near the town centre, services heading in other directions (eg the X5, 905, 50) do not and all passengers have no option to the bus station. Bradford is the same, for example the 268, 283, 425 in from the south gives no option to the bus station but services heading north have stops in the town centre. Burnley another example. Preston is splendid and well worth keeping, it isn't far from the shops, but again buses heading east do not stop anywhere else.
Stratford was mentioned, that used to have a bus station but it was a walk from the shops, now pretty much all services get closer to the shops. At St Albans and Tunbridge Wells, also mentioned, all services serve all parts of the town centre and overlap, which is good for proximity but not so good for waiting facilities etc and the other benefits a bus station can provide, plus of course terminating services stand on the streets. I think Darlington works OK, the stops are all pretty close together although services heading out to the south start in front of the town hall. Where would you put a bus station now?
Colne on the other hand is a waste of time, it would be much better to have a bus contraflow on Market Street and close the bus station.