Tiff's or tagged image file format is a lossless format and so will not lose any image information when you move from one program to another. Jpeg or Joint photographic experts group, is a lossy format and will lose some detail as you compress it. However as Pmermino said you can alter the compression depending on the size vs quality you require. If you want the best quality, I'd save renders as .tif then import to photoshop or whatever and convert to .jpg Don't forget that each time you save a jpeg it looses more information until the compression artifacts are quite visible, so try to make the conversion to jpeg the last process. Having said all that, I agree with Pmermino that 70% jpeg is quite OK for the web.