The media world nowadays doesn’t work anymore without detailed mock-ups (aka sample produced demos) of cues. The times when composers just presented their ideas on the piano and the directors trusted them that it will sound great in the end are over.
If a project eventually will be recorded with real players, there are several things that you need to take into consideration with your demo mock-ups:
You want to sell your track to your client but you don’t want to make the demo so good that he/she might be asking why to record live players at all. This problem often arises with less experienced filmmakers. You also want to be time effective on them. One can polish a mock-up forever but especially when you do them by yourself, your main focus regarding time should be on composing rather than producing demo material. Another important issue is to not raise unfulfillable expectations with your client. If you only have budget for a small orchestra, don’t use all the “epic huge section” samples on your demos. Otherwise the dissappointment of your client after the recording could become really problematic.
Often, before a project I tend to present to the client music from former projects, preferably pretty bad demo mock-ups compared to the final recording of the cue. This gives them an idea of how it’s gonna sound in the end. But this is also very depending on the musical knowledge of your client. With some clients I can simply give them an audio of the pretty basic sounds of Sibelius and they know how it’s going to sound in the end while with others I’m producing very detailed mock-ups. But in general, always make sure to let your client long for more to justify spending a lot of money on a real recording.