It’s generally recommended that justified text (set flush to both the left and right margins) should be avoided on web pages. There are two main reasons for this.
Fully justified web copy is difficult to read
Justified text makes it more difficult for the reader’s eyes to track their location on the page, as well as pick out words, phrases and so on. Plus, the irregular spacing used between words in order to justify the copy means that it can’t be read ‘smoothly’.
Browers can’t handle justified text very well
The level of control in producing justified text with printed page layout programs isn’t possible with web pages, where copy can be viewed in a different way on every browser according to an individual’s settings. This leads to word spacing and hyphenation issues, as well as other problems.
So, left-justified text is still the most readable option. It doesn’t affect word spacing and it also gives a ragged right-hand margin. This makes the page easier to read, as well as adding visual interest.