do i need to set length for every poco property in Entity Framework Code First ? if i dont set stringLength or maxlength/minlength for a property , it will be nvarchar(max) , how bad is nvarchar(max) ? should i just leave it alone in development stage , and improve it before production ?
You should define a Max length for each property where you want to restrict the length. Note that the nvarchar(max) data type is different from the nvarchar(n) datatype, where n is a number from 1-4000. The max version that you get when you define no max length is meant for large blocks of text, like paragraphs and the like. It can handle extremely large lengths, and so the data is stored separately from the rest of the fields of the record. nvarchar(n), on the other hand, is stored inline with the rest of the rows.
It's probably best to go ahead and set those values as you want now, rather than waiting to do so later. Choose values that are as large as you will ever need, so you never have to increase them. nvarchar(n) stores its info efficiently; for example, a nvarchar(200) does not necessarily take up 200 characters of space; it only uses enough space to store what is actually put into it, plus a couple extra bytes for saving its length.
So whenever possible, you should set a limit on your entity's text fields.