Hi Luke_abc,
The main advantage of NDEF is interoperability by giving semantic to the data. Android and Apple iPhones will read nowadays NDEF messages automatically. Android phones will know how to interpret most of the data contained in NDEF. iPhone will automatically open a few types of NDEF messages.
If you are using only one type of tag and only some proprietary data then probably no need to use NDEF, just make sure that your data is not by mistake interpreted as NDEF.
If you are using various different tags then it may become interesting to at least NFC Forum capability containers and maybe put proprietary TLVs into the NDEF file or use some mime-types. This helps you to manage different memory layouts, memory access etc. for most memory tags.
I hope this gives you some ideas what to consider.
BR, Ulysses