I recently started adding some older manual lenses to my collection. Modern autofocus lenses are fine, but at times, they have their limitations. The camera nearly always tries to focus on an object nearest to it, which really isn't much use when trying to photograph wildlife through a bunch of leaves or grass. OK, I could switch to manual focus, but modern lenses just aren't that user friendly in manual mode. Bring on the older stuff!
Older lenses have a much greater "throw" when it comes to focussing - you have to turn the focus ring much further between macro and infinity. This allows for more accurate focussing. Unfortunately, modern digital cameras don't have the neat focussing screens found on older manual film cameras, so focussing accurately does take a bit of getting used to, but it is possible.
I won't go into the hows and wherefores about mounting vintage or legacy lenses on modern digital cameras, as there are plenty of other sites and blogs covering that subject.
Suffice to say, you can get good quality legacy glass for much less than modern digital lenses. Search through online web auctions, charity shops, boot fairs, yard/garage sales etc., and you'll find plenty to choose from. Not all old lenses work with all digital cameras, Nikon users are severely limited in this area, unless they use optical adapters, which introduce extra glass to achieve infinity focussing. Canon users by comparison, can use most legacy glass, apart from, ironically, pre EOS (EF) Canon lenses.
Anyway, I started my collection with a Soviet era Russian MIR-1B. A 37mm f2.8, Zeiss Flektogon derived, semi-clone.