In reply to tom_in_edinburgh:
The ropes at some walls are barely long enough for doing that...
No, I've never heard of tying on at both ends indoor, particularly as for any given indoor route when top-roping there'll be one side of the rope that's better to use than the other to prevent it getting in the way.
Or do you mean tie to krab and clip? Yes, that's only used for groups (and then not always), as it's less safe (more to go wrong/forget).
Neil