Cascode Amplifier Biasing Sequence
In order for the MESFET \$\mathrm{FET_1}\$ to work in saturation region, you should require that 
$$
|V_{DS_\mathrm{FET_1}}|\ge |V_{P_\mathrm{\,FET_1}}|+|V_{GS_\mathrm{FET_1}}|, \label{1}\tag{1}
$$ 
where \$V_{P_\mathrm{\,FET_1}}\$ is the pinch off (threshold) gate-source voltage of the MESFET. This implies that the quiescent value of \$V_{GG_2}\$ must be chosen in such a way that \eqref{1} is satisfied, and in turn this implies that
$$
V_{GG_2}\gg V_\gamma,
$$ 
where \$V_\gamma\$ is the threshold voltage of the \$\mathrm{FET_2}\$ Gate-Source GaAs Schottky junction: normally, this is not a problem since when \$V_{DS_\mathrm{FET_1}}\$ is at its quiescent value \$V_{DSQ_\mathrm{FET_1}}\$, then 
$$
V_{GSQ_\mathrm{FET_2}}=V_{GG_2}-V_{DSQ_\mathrm{FET_1}}&lt;0
$$
However, if you apply \$V_{GG_2}\$ before applying \$V_{GG_1}\$ then, since \$V_{DS_\mathrm{FET_1}}\$ is still nearly zero, the \$\mathrm{FET_2}\$ Gate-Source GaAs Schottky junction would became forward biased with a high value of gate current \$I_{G_\mathrm{FET_2}}\$ which would permanently damage the device: in sum in order to avoid permanent damages to the MESFETs, it is better to follow the recommended biasing sequence.