In my opinion, risers can be used to get the bars in the "attack position" for a specific rider, on a specific bike, with a specific bar. Some people can tend to go overboard with the riser/tall bars for my comfort zone.
I am 6-2 and below are my set ups current and some past:
GasGas 280 pro- no risers, tag fat bar trials bend.
1974 Honda TL 125- custom machined 25 mm riser blocks with 6" domino trials bend bars.
Husaberg FE 450 and FE 570 - no risers, stock Magura's, stock bar setting, with KTM hard parts PDS bar mounts.
KTM 950- stock bars no risers.
03 drz 400- risers 1" high, 1" forward, RM low bend renthal fat bars.
04 RM 250- no risers, rg3 clamp, standard position, RM low bend renthal fat bars.