All those years ago we used peat in the garden, and if you ask any horticulturalist the only reason was it conditioned the soil a little but was very cheap! These days I never use peat. Compost is much better, though I used to get a lot of spent hops from a local brewery to give sandy soil a little body.
Sowing under cloches is always helped if you add compost to the soil, it creates a crumbly bed, and the cloche itself adds about 5C to the air temperature on a good day, so you can get some plants off to a good start.
Of course, modern cloches are plastic, and the double walled ones are very good insulators, so you can get salad crops going – I often grow in pots and cover them with a cloche, a huge outdoor propagator.