...as one who does(occasionally)... it is very much the minority who, when the conditions are right, may use a cloud climb to provide them with an advantage. There are certain criteria which should be applied and these are defined in the Laws and Rules for glider pilots:
"No glider shall enter cloud within a radius of 5 nautical miles of a gliding site, except from at least 200 feet from below the lowest part of the cloud.
No glider shall enter cloud unless all its occupants are wearing parachutes and have been instructed in their use.
Additionally it is standard practice to announce your intention to enter cloud on which ever frequency you are operating on giving height (QNH), and location and then changing frequency to 130.4. Once on 130.4, this message is repeated and then the height called at every 500'QNH. Once clear of cloud call "[Callsign] clear of cloud' before changing to en-route frequency.
Cloud flying is not for the faint hearted or novice, and pilots really should be of sufficient standard that their general flying is intuitive - but there are times when it can prove useful, especially on log distance flights or in competitions.
However, not only do you need to have the skills to keep a glider in controlled and balanced flight on instruments (preferably turning to gain height) but also have a full of a number of other factors to consider - before you even enter the cloud:
At what height the zero degree isotherm is (when icing may start),
What other gliders were in the vicinity prior to entering cloud,
Does the aircraft you are flying speed limit below VNE with full airbrakes out and at what dive angle?
Is there any controlled airspace above you - to name but a few!
My first few excursions (as a P2) into cloud flying were scary, and resulted in my pulling the airbrakes out and descending below cloud. In terms of frequency, I've flown over 4000kms this year, but only taken 2 cloud climbs (although a 3500 ft climb in cloud, having entered it from a 3800 ft cloud base, was particularly satisfying, if not just a tad twitchy!)