So this is a tip people usually don´t know but you can make your PSD files a lot smaller if you just hide the layers before saving it!
To hide a layer just click on the "eye" icon on the left of your layer name:
After you have hidden all the layers just save your document as a psd. And actually you can make it even more smaller... you just need to compress it using Winrar or other Compressor program.
Look at this example of a 4000x6000 pixel work i've made to see how much you can save:
- Psd with layers visible - 154 MB
- Psd with layers hidden - 94 MB
- Psd with layers hidden and compressed with WinRar - 60,9MB