In brief we may say that there are three scenarios for fasting at the end of Sha'ban: The first scenario is when a person fasts at the end of Sha'ban with the intention of being on the safe side and not missing the first day of Ramadan. This is forbidden.
The second scenario is when a person fasts with the intention of fulfilling a vow or of making up a day of Ramadan that he missed or as an act of expiation (Kaffarah), etc. This is permissible according to the majority.
The third scenario is when this is purely a voluntary fast. This is regarded as Makruh by those who said that we should differentiate between Sha'ban and Ramadan by not fasting for a while. Among those who said this was al-Hasan, may Allah have mercy on him.
If it happens to coincide with a day when a person habitually fasts, Malik and those who agreed with him permitted this, but Ash-Shafi’i, al-‘Awza’i, Ahmad and others made a distinction between cases where it is a fast which a person habitually observes or otherwise.
In conclusion, the Hadith of Abu Hurayrah, may Allah be pleased with him, quoted above is what we should follow according to the majority of scholars. It is Makruh to observe a voluntary fast one or two days before Ramadan for those who do not habitually fast on those days and who have not previously fasted until the end of Sha'ban.