Yes - in my opinion green manure is 'a good thing' - depending on what you choose: keeps down the weeds, makes nutrients locked in the subsoil available to new crops, reduces the need for brought in (and bought in) manure, adds nitrogen to the soil after a nitrogen-depleting crop, starts to break up a compacted 'pan', adds humus to the soil etc etc.
As an added benefit green manures often force you not to over-cultivate your land (e.g. if I follow new potatoes (March) with leeks (July) then Peas (February/March) then kale (June/July) that bit of ground has been cultivated with two crops per year without a break for a couple of years. If I then (say) put buckwheat once the kale is over this give the soil a break over the summer/autumn in time to put in a crop of overwintering alliums/garlic. I appreciate that this crop rotation is not necessarily 'perfect' from a text-book standpoint, but it is probably a realistic one for a lot of us.
You need to match the green manure to your soil and growing conditions.
What the uber-fans of green manures don't always tell you is just how hard some of them can be to dig in (e.g. Hungarian Grazing Rye), and that the weeds that do grow often get so tangled up with the manure that it's nearly impossible to pull them out when digging in.
A nice easy one to get you started is field beans when you do your winter digging - early November works well in my area - you can then hack them down (with a 'slasher - great fun) as they start to flower (at least a couple of times) and still get a late spring/early summer crop in - they're not too difficult to dig in either and if you leave them really late before digging in then judicious application of weedkiller (or careful digging/weeding) will address most of the thistle/bindweed problems for the rest of the year.
SS