Use of surname aliases

[Fishing4Fishers]

I recently found an ancestor's Last Will and Testament dated in 1793 where he describes himself as "Thomas Roberts otherwise Hayward of Ampney Crucis" and leaves the bulk of his estate, "Two Freehold Messuages or Tenements" to one of his sons, "David Roberts otherwise Hayward."  Earlier records that apparently pertain to this same family (I haven't proven the link, but they are in the same two villages, Ampney Crucis and Down Ampney) use the surnames Roberts alias Hayward, or Hayward alias Roberts.  Is there anyone out there with genealogical expertise in old English records that can tell me why this use of aliases occurs in what appears to be multiple generations?  Does it have to do with preserving inheritance to land?  This is not a wealthy family. 

[stanmapstone]

 Alias means "also known as".  In other words the person was known by more than one name. Aliases were used in cases of illegitimacy, upon the remarriage of a parent, [i.e. if a mother remarried, her children might take the name of their new stepfather, with their original name as an alias - or vice-versa]; upon inheriting property from a female relative, etc.; to differentiate between different holders of common surnames; to indicate stepchildren or fostered children. In some cases the alias form was inherited for several generations, and was similar to a double barrelled surname Discovering the reason for an alias is not straightforward, and each case has to be treated on it's merits. Even in cases of illegitimacy there is no rule whether the father's or the mother's name was given first.

Stan

[youngtug]

Was a fairly common practice at one time;
https://www.familysearch.org/wiki/en/Use_of_Aliases_-_an_Overview

[Fishing4Fishers]

Thanks, Stan and "youngtug."  I read the article at Family Search, and it seems there are many possibilities.  I live in Iowa in the U.S., and my only familiarity with the use of aliases involves criminals.  (I worked in the court system for many years.)  I was stuck on the Hayward family (which married into the Fisher family) until another descendant in England saw my family tree online and contacted me with the information that Thomas Hayward used the surname alias Roberts, and I found his Will after doing a search at Ancestry.com using the name Thomas Roberts, rather than Thomas Hayward.