It is not recommended i guess its a matter of our choice,altcoins were more cheap compared to bitcoins.If you see some potential coins and has big possibilities to boom in the market then probably better hodl your altcoins rather than selling it to buy bitcoins.
On the other hand bitcoin has never failed us,its consistency in the market remains to be the toughest cryptocurrency of all time and i think that it is also advisable to own bitcoins,but you need to find your way to  buy bitcoins,but not selling potential coins.