In any secret sharing scheme we have to develop step by step. After constructing such scheme we need to reduce share size. Why? e.g. Robust secret sharing scheme is modified Shamir secret sharing scheme with error correcting REED SOLOMON codes. In order to gain near optimality we need to reduce share size. Why? what is optimal in any secret sharing scheme? How do i know it's optimal? From cheater resilient (t,$\delta$) robust secret sharing scheme ,it says that the scheme is optimal. How do they know?
Optimality is actually not a well-defined term for secret sharing, and can refer to a number of different issues. First, one issue that is often considered is the size of the share that each party holds in the scheme. If the size of a party's share equals the size of the secret itself, then the secret sharing scheme is called ideal. (Formally, we don't talk about "size" but that the shares comes from the same domain as the secret.) Shamir's secret sharing scheme is ideal.
Other issues which come up are the threshold: how many parties are needed to reconstruct the secret versus against how many parties security holds, what the threshold is for active/passive security and so on.
In short, the paper should define what they mean by optimal, and especially regarding what parameters.